It's pretty much awful over here all year round!
The early part of the summer is when we get the best weather usually, between april and the end of may (well, it's been like that for the last few years, before decending into a sort of monsoon season from the second week in june until august!).
Another good time to come would be around now, september-october. It's starting to get cold, but it's no where near as bad as wintery coldness, but you frequently get a nice bit of sun.
God has a cruel way of treating those who are in school in Ireland. The weather turns for the worse immediatly after they get their holidays, and rapidly improves once they're back!
In terms of courses, theres literally hundred of fabulous courses here. Just don't go the the K Club (where they played the Ryder Cup a few years ago, it's very american, and not really traditionally irish. Some good ones include Royal Co. Down, Portmarnock, Ballybunion, but i'm sure other people have other suggestions.
For nightlife, I can't really vouch for anywhere apart from Dublin itself, seening Ive never really been involved in a scene outside the capital. But lots of the best nightclubs are around the St. Stephen's Green - Harcourt St area, which is just south of the river liffey. Dublin's a small enough city, so you won't be getting lost anywhere.
Enjoy your stay!